One example of methods of adjusting the electric characteristics of a high frequency circuit in which a predetermined conductive pattern is disposed on a dielectric substrate is a method of adjustment by affixing dielectric tape to the dielectric substrate. For example, see Japanese Unexamined Patent Application Publication No. 9-238002 (Patent Document 1), Japanese Unexamined Patent Application Publication No. 59-230302 (Patent Document 2), and Japanese unexamined utility model Application Publication No. 56-96708 (Patent Document 3).
FIG. 1A is a plan view of a band-pass filter illustrated in Patent Document 1, and FIG. 1B is a cross-sectional view thereof. The band-pass filter is configured as a three-stage filter having a parallel coupled line structure using a half-wave resonator. A ground conductor 2 is disposed on the back side of a dielectric substrate 1. A half-wave resonator 3 having a three-stage configuration using microstrip lines is disposed on the front side of the dielectric substrate 1. An input pattern portion 4 and an output pattern portion 5 formed using microstrip lines connected to the above microstrip lines are disposed on the input side and the output side of the half-wave resonator 3, respectively. Dielectric tape 6 is affixed to the front side of the dielectric substrate 1 in a region other than the input pattern portion 4 and the output pattern portion 5. The dielectric tape 6 is formed from a thin dielectric film, and an adhesive is applied to the back side thereof.
The affixation of the dielectric tape 6, so as to cover the resonator 3 on the front side of the dielectric substrate 1, as described above, enables adjustment of the center frequency of the filter.